JPH0697519B2 - Magneto-optical recording device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording apparatus using a Curie point writing type magneto-optical recording medium which can be read by utilizing the magnetic Kerr effect.

[0002]

2. Description of the Related Art A magneto-optical recording medium is known as an erasable optical memory. The magneto-optical recording medium has an advantage that high-density recording and non-contact recording / reproducing are possible as compared with a magnetic recording medium using a conventional magnetic head, but on the other hand, the recorded portion must be erased once before recording. It has the disadvantage that it must be magnetized in one direction. As a magneto-optical recording device for compensating for this drawback, there are a magneto-optical recording device in which a recording / reproducing head and an erasing head are separately provided, and a device which irradiates a continuous laser beam and simultaneously records while modulating a magnetic field applied. is there. However, in the former case, these magneto-optical recording / reproducing devices are large-scaled and costly. Further, the latter has a drawback that high speed modulation cannot be performed. For this reason, the applicant has previously proposed a magneto-optical recording method capable of overwriting similar to a magnetic field recording medium by simply adding a magnetic field generating means having a simple structure to the conventional apparatus configuration. (Japanese Patent Application No. 61-158787)
No .: Basic application for priority claim application in Japanese Patent Application No. 62-20384). That is, the first magnetic layer having a low Curie point (T _L ) and a high coercive force (H _H ), and a Curie point (T _H ) and a low coercive force (H _L ) which are relatively higher than those of this magnetic layer.
Using a magneto-optical recording medium having a two-layered perpendicularly magnetized film having a second magnetic layer on a substrate, a coercive force H _{L is applied} to the medium at a position different from the recording head. Magnetic field B having a coercive force H _H sufficient to magnetize the second magnetic layer in one direction and does not reverse the magnetization direction of the first magnetic layer, and then a bias is applied by the magnetic head. By applying a magnetic field and at the same time irradiating laser power enough to raise the temperature of the medium to near the low Curie point (T _L ), the magnetization direction of the first magnetic layer can be maintained without changing the magnetization direction of the second magnetic layer. the first type of pre-recorded or to align the stable orientation for the second magnetic layer, it at the same time high Curie point by applying a bias magnetic field (T _H) near to the medium is irradiated with a laser power of only heating Reverses the magnetization direction of the second magnetic layer. The second kind of pre-recording, in which the first magnetic layer is magnetized in a stable direction with respect to the second magnetic layer at the same time, is performed according to a signal, and then the medium is moved,
By passing the magnetic field B through the prerecorded bits, the magnetization direction of the first magnetic layer and the second magnetic layer of the bit formed by the prerecording of the first type does not change and the second type does not change. For the bit formed by the preliminary recording, the direction of magnetization of the second magnetic layer is reversed in the same direction as the magnetic field B, and the direction of magnetization of the first magnetic layer is left unchanged and binary recording is performed. It is a thing.

[0003]

Although the overwriting is enabled by the above-mentioned method, in order to improve the stability of the recording bit, it is provided between the first magnetic layer and the second magnetic layer of the magneto-optical disk. When a similar process is carried out by providing a third magnetic layer whose easy magnetization direction is the in-plane direction, there is a risk that recording noise will occur when the magneto-optical disk passes over the magnetic field generated from the magnetic field generation section. There is. An object of the present invention is to remove as much as possible the in-plane component of the magnetic field from the magnetic field generation unit that is separated into the component in the vertical direction of the substrate of the magneto-optical disk and the component in the in-plane direction to reduce recording noise. An object is to provide an overwritable magneto-optical recording device.

[0004]

According to the present invention, a magnetic shield plate is provided between a magnetic field generating section and a magneto-optical recording medium, and the magnetic field generating section has an opening at a portion where a magnetic field is applied to the magneto-optical disk. By disposing the mask provided with the portion so as to cover the magnetic field generation portion, it is possible to prevent the in-plane component of the magnetic field from the magnetic field generation portion from being applied to the magneto-optical recording medium.

The recording apparatus of the present invention naturally includes a recording apparatus provided with a reproducing means.

Overwrite recording by the recording / reproducing apparatus of the present invention is performed at a low Curie temperature ( _TL ).
And a first magnetic layer having a high coercive force (H _H ) and a second magnetic layer having a relatively high Curie temperature ( _TH ) and a low coercive force ( _HL ) as compared with the magnetic layer. A magnetic film,
The Curie temperature provided between the first magnetic layer and the second magnetic layer is T
It is between _L and T _H, easy magnetization direction of the third magnetic layer in the plane direction rare earth - transition metal alloy film and the Japanese Patent Application Sho 62-20384 DISCLOSURE process using a magneto-optical recording medium comprising The process is similar to. The bias magnetic field during recording is set as follows.

In the first type of preliminary recording, since the force (exchange force) that the magnetization of the first magnetic layer tries to align in a direction stable with respect to the direction of the magnetization of the second magnetic layer, the bias magnetic field is originally intended. Is not necessary. On the other hand, in the second type of preliminary recording, the bias magnetic field is set in a direction to assist the magnetization reversal of the second magnetic layer. And for records that can be overwritten, the first type,
It is preferable that the magnitude and direction of the bias magnetic field are set to be the same in the preliminary recording with both laser powers of the second type (otherwise, the bias magnetic field must be modulated at the recording frequency).

In the magneto-optical recording medium used in the above process, the third magnetic layer provided between the first magnetic layer and the second magnetic layer and having the in-plane easy magnetization direction is the first magnetic layer and the second magnetic layer. It serves to limit the orientation of the respective magnetizations of the magnetic layer in the most stable orientation. This orientation force is generated because spins of the same atom in each magnetic film tend to be parallel to each other, so that the orientation force is generated through the third magnetic layer in which spins are easily oriented in the in-plane direction. Is hard to work with. By providing this third magnetic layer, the stability of recorded bits is improved. That is, the magnetization of the third magnetic layer tends to be oriented in the in-plane direction, and when recording is not performed, the magnetic coupling between the first and second magnetic layers is weakened to stabilize the recording bit. When the composition of the third magnetic layer is set to a region in which the ratio of the rare earth element is larger than the compensation composition, the magnetization decreases as the temperature rises during recording and the anisotropy in the direction perpendicular to the substrate surface increases. The magnetic coupling (exchange coupling) of the second magnetic layer can be made strong.
This makes it possible to stably perform the first type and the second type recording. The characteristics of each magnetic layer are as follows.
That is, normally, T _L of the first magnetic layer is 70 to 180.
C, H _H is 3 to 15 KOe, and T _H of the second magnetic layer is 100.
˜400 ° C., H _L is 0.3 to 2 KOe, Curie point of the third magnetic layer is 80 to 250 ° C., and the applied magnetic field when the magnetization is saturated in the direction perpendicular to the substrate is preferably in a range larger than H _L. . As a material for each magnetic layer, a material exhibiting perpendicular magnetic anisotropy and exhibiting a magneto-optical effect can be used.
dCo, GdFe, TbFe, DyFe, GdTbF
e, TbDyFe, GdTbFeCo, TbFeCo,
An amorphous alloy of a rare earth element such as GdTbCo and a transition metal element is preferable.

Next, in order to clarify the operation of the present invention, the stability of the bits recorded in the above process and the cause of recording noise will be described.

The bit formed by the first type of preliminary recording has no magnetic layer which causes magnetization reversal no matter how many times it passes through the magnetic field B. Therefore, the first, second and third magnetic layers are placed in a stable state by the preliminary recording. However, when the bit of the second magnetic layer formed by the second type of preliminary recording passes through the magnetic field B, the magnetization is reversed in the direction of the magnetic field B. On the other hand, since the coercive force of the first magnetic layer is larger than the magnetic field B, the magnetization reversal does not occur. Furthermore, since the third magnetic layer is also easily magnetized only in the in-plane direction, the magnetic field B should not cause magnetization reversal.

However, when the magnetic field in the in-plane direction of the substrate is applied, the magnetization of the third magnetic layer is reversed even with a magnetic field of several hundred Oe.
Therefore, when the magnetic field B is repeatedly passed, the magnetization reversal of the third magnetic layer occurs due to the component of the magnetic field B in the in-plane direction of the substrate. In this case, if the first magnetic layer has a component that is easily magnetized in the in-plane direction of the substrate, strong magnetic coupling works, and the magnetization of the first magnetic layer in the in-plane direction of the first magnetic layer is gradually increased during reproduction. The magnetization reversal of the component occurs, which causes the recording noise.

Therefore, it is necessary to devise to minimize the magnetic field component of the magnetic field B in the in-plane direction of the substrate.

To this end, it is effective to remove the magnetic flux that reaches the magneto-optical recording medium from the magnetic field generating portion. In view of this point, in the present invention, a mask of a magnetic shielding plate having an opening is provided between the magnetic field generation unit and the recording medium to remove the magnetic flux incident on the recording medium in an oblique direction, and to eliminate the magnetic field generation unit from the opening. Is applied to the recording medium.

Further, if a similar magnetic field generator of opposite polarity is provided on the opposite side of the magnetic field generator with respect to the recording medium, the effect of removing the magnetic flux arriving due to wraparound is further enhanced.

[0015]

Example A magneto-optical disk was manufactured as follows. First, Si (silicon) was provided as a protective layer in a thickness of 500Å on a polycarbonate disk substrate on which pre-group and pre-format signals were engraved. Next, a first magnetic layer Tb ₁₂ GFe ₇₈ (atomic ratio) was provided to a thickness of 300Å.
This first magnetic layer has T _L = about 150 ° C. and H _H = about 8 KOe.
Thus, the sublattice magnetization of the Fe atom was larger.

Next, a third magnetic layer Tb ₃₅ Fe ₆₀ Co ₅ (atomic ratio) was provided to a thickness of 150Å. Curie temperature is about 17
The magnetization reversal occurred at 0 ° C. and the in-plane direction was the easy axis of magnetization, and 400 G in the in-plane direction. An external magnetic field of about 3.0 KOe was required to orient the magnetization in the perpendicular direction.

Next, the second magnetic layer Tb_{twenty four}Fe₆₈Co₈ (atom
Ratio) to a thickness of 300Å. T _H = Approx. 180 ° C, H
_L = About 1.0 KOe, the sub-lattice magnetization of the second magnetic layer is Tb
The atom was bigger.

Next, Si (silicon) is used as a protective layer 10
It was set to a thickness of 00Å.

Finally, the above substrate was bonded to a polycarbonate bonding substrate using a hot melt adhesive to prepare a magneto-optical disk.

The magneto-optical disk 11 produced in this way
A recording / reproducing experiment was conducted by using the magneto-optical disk recording / reproducing apparatus of the present invention illustrated in FIG.

The magneto-optical disk 11 was set on the rotary shaft of the spindle motor 3. In this device, the light source 4
Light emitted from the laser beam passes through the optical modulator 5 and the polarizer 13, is reflected by the half mirror 6, and is focused on the magneto-optical disk 11 through the objective lens 7 whose vertical position is controlled by the coil 10. . Further, the reflected light passes through the objective lens 7, the half mirror 6, and the analyzer 8 and is guided to the light conversion element 9 to generate a reproduction signal. Further, the present invention is
It has a magnet 12 for generating a bias magnetic field during recording, a magnet 1 for generating a magnetic field, and a mask 2 for magnetically shielding. In addition,
The mask 2 is provided so as to cover the magnetic field generating portion 1 in order to shield the surroundings of the magnetic flux generated by the magnetic field generating portion 1. The mask 2 has an opening at a portion where the magnetic field generating portion 1 applies the magnetic field B to the magneto-optical disk 11. Section is provided.

Magnetic field 2 KOe from the magnetic field generator 1 to the substrate surface
While passing a region (less than 200 Oe into the substrate surface) at a linear velocity of 7 m / sec, a laser beam with a wavelength of 830 nm focused on a diameter of about 1 μm at a duty ratio of 50% at frequencies of 1 MHz and 2 MHz. Recording was performed with a binary laser power of 4 mw and 8 mw under a bias magnetic field of 150 Oe while modulating. After that, 1.0m
When a signal was reproduced by irradiating a laser beam of w, a binary signal could be reproduced. No signal deterioration or noise increase was observed even after repeated reproduction. In this experiment, the magnet used for the magnetic field generating unit 1 is a 10 mm square made of sintered ferrite, and a 10 mm square portion faces the magneto-optical disk 11. The distance between the magnet and the disk substrate was 10 mm. Further, the opening of the magnetic shielding plate has a square shape of 3 mm, and
The distance from 1 was set to 3 mm, and the opening was set on the center of the magnet.

Next, by changing the size of the opening provided in the mask and the distance between the mask and the magneto-optical disk, the vertical magnetic field applied to the substrate surface of the magneto-optical disk and the in-plane when the above-mentioned magnetic field is applied. The results of the experiment for measuring the directional magnetic field are shown in Table 1 below. As a comparative example 1, the experimental results in the case where the mask is not attached are described. The vertical magnetic field and the in-plane magnetic field are 2800 (Oe) and 380 (O
e), and noise was seen during reproduction.

[0024]

[Table 1] In this way, when the mask is not provided in Comparative Example 1,
The in-plane magnetic field component of the disk substrate from the magnetic field generation unit 1 increased, and noise increased during reproduction. However, in Examples 1-1 to 1-5 in which the mask is provided, noise increases during reproduction. There wasn't.

[0025]

As described above, according to the present invention, a mask is provided to prevent the in-plane direction component of the magnetic field from the magnetic field generator from being applied to the magneto-optical recording medium. It has become possible to reduce.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a magneto-optical recording apparatus of the present invention.

[Explanation of Codes] 1 magnetic field reproducing magnet 2 mask 3 motor 4 light source 5 light modulator 6 half mirror 7 lens 8 analyzer 9 light conversion element 10 coil 11 magneto-optical disk 12 bias magnetic field generator 13 polarizer

Claims (1)

[Claims] 1. A first magnetic layer made of a perpendicular magnetic film, a Curie temperature relatively higher than that of the first magnetic layer, and a coercive force lower than those of the first magnetic layer, and the perpendicular magnetization exchange-coupled with the first magnetic layer. A magneto-optical recording medium composed of a second magnetic layer formed of a film and a third magnetic layer provided between the first and second magnetic layers and having an easy magnetization direction in the in-plane direction for adjusting the strength of the exchange coupling. A means for irradiating a light beam whose intensity is modulated according to the recording signal,
A first magnetic field generating means for applying a bias magnetic field in the vicinity of the light beam irradiated portion of the medium; and a second magnetic layer for orienting the magnetization direction of the second magnetic layer in a predetermined direction prior to the irradiation of the light beam.
In the magneto-optical recording device including the magnetic field generating means, there is an opening that is arranged between the second magnetic field generating means and the medium and that transmits a part of the magnetic flux from the second magnetic field generating means. 2. A magneto-optical recording apparatus having a mask formed of a magnetic shielding material that prevents the in-plane direction component of the magnetic field generated by the magnetic field generating means from being applied to the medium.